1. Field of the Invention
The present invention relates to an optical semiconductor element such as a light emitting diode and a manufacturing method thereof.
2. Description of the Related Art
Optical semiconductor elements such as light emitting diodes have been made to have high output power due to recent years' advance in technology. Accordingly the amount of heat generated in the optical semiconductor element has increased, and hence there are the problems of reduction in luminous efficiency, degradation of a semiconductor film, and the like. In order to solve them, a configuration is taken where the growth substrate of relatively low thermal conductivity such as a sapphire substrate used for semiconductor-film crystal growth is removed and where instead a substrate of relatively high thermal conductivity is used to support the semiconductor film.
Further, a plurality of protrusions deriving from the crystal structure of the semiconductor film are formed by performing chemical etching on the surface of the semiconductor film exposed by removing the sapphire substrate, and thereby a light extraction structure is formed in the light extraction surface. By this means, the portion of light that is totally reflected at the light extraction surface can be reduced, and hence the light extraction efficiency can be improved. For example, by performing wet etching with an alkali solution on the C-plane of a GaN-based semiconductor film, a plurality of six-sided pyramid-shaped protrusions deriving from a wurtzite-type crystal structure can be formed in the C-plane. The protrusions deriving from a crystal structure are referred to as micro-cones.